Hi Jamian
It does appear that you can still get the foam pads for the Form 1 headphones, I got two sets just two months ago from our local B&O dealer. However, they are a diminishing resource and I was told that it is going to be difficult to get any more if needed. Cost in Oz was about A$25 for the kit of two earpieces and two temple rests. Part number was 3917087 so it may still be worth contacting your local agent.
The dimensions of the earpiece is about 43mm square by about 8mm thick. The temple support has a 37 x 15 mm base and extends about 17mm high.
I tried some tests with some foam that I had laying around, 6mm and 12mm thick. My personal preference was for the thicker foam and I was happy with the audio quality. Now I just have to find the same sort of stuff in black!!
Hope that helps a bit
Regards
Geoff